Various classifications have been proposed for sleep disorders based on symptoms and causes, as given below for example.
(i) The Diagnostic Classification of Sleep and Arousal Disorders (DSCAD) was proposed in 1979 by the Association of Sleep Disorders Centers (ASDC) of the United States (Sleep, Vol. 2, p. 1-154, 1979). This is the earliest classification that grouped sleep disorders in view of “Disorders of Initiating and Maintaining Sleep (DIMS)”.
DSCAD classifies sleep disorders broadly into nine categories: (1) psychophysiological insomnia; (2) sleep disorders associated with mental disorders; (3) sleep disorders associated with a regular use of drugs and alcohol; (4) insomnias associated with sleep-induced breathing disorders; (5) sleep disorders associated with nocturnal myoclonus and restless legs syndrome (RLS); (6) sleep disorders by other disorders, drugs, and environmental conditions; (7) childhood onset insomnias; (8) other types of insomnia; and (9) sleep abnormalities with no symptoms of insomnia. Each of these categories is based on the state of disorder.
(ii) The International Classification of Sleep Disorders (ICSD) was reported in 1990 by the American Sleep Disorders Association (ASDA) (ICSD-International classification of sleep disorders: Diagnostic and coding manual, Diagnostic Classification Steering Committee, Thorpy M J, Chairman. Rochester, Minn.: American Sleep Disorders Association, 1990), and was revised in 2000.
ICSD classifies sleep disorders broadly into four categories: (1) dyssomnias comprising disorders that are primarily disorders of sleep per se [for example, intrinsic sleep disorders such as narcolepsy, extrinsic sleep disorders, and circadian rhythm sleep disorders]; (2) parasomnias comprising disorders of abnormal behaviors that occur during sleep (also known as abnormal behavior during sleep) [arousal disorders, sleep-wake transition disorders, parasomnias usually associated with REM sleep, and other parasomnias]; (3) sleep disorders associated with medical/psychiatric disorders [sleep disorders associated with mental disorders, sleep disorders associated with neurologic disorders, and sleep disorders associated with other medical disorders]; and (4) proposed sleep disorders [for example, short sleeper, long sleeper, subwakefulness syndrome, and the like]. To this date, this classification includes about 90 categories of sleep disorders. Currently, further classifications have been made continuously based on etiology.
(iii) According to the International Classification of Diseases, Tenth Edition (ICD-10) (1992), which have been published by World Health Organization (WHO), sleep disorders are classified into (1) nonorganic sleep disorders (F51: for example, nonorganic insomnia, nonorganic hypersomnia, sleep walking, sleep terrors, nonorganic disorder of the sleep-wake schedule, nightmares, and the like); (2) sleep disorders [G47: for example, sleep apnoea, disorders of initiating and maintaining sleep (insomnias), disorders of excessive somnolence (hypersomnia), cataplexy, narcolepsy, cataplexy attacks, disorders of the sleep-wake schedule (such as irregular sleep pattern, sleep rhythm disorder, and delayed sleep phase syndrome), and the like]; (3) other respiratory conditions originating in the perinatal period (P28: for example, primary sleep apnoea of newborn, and the like); and (4) personal history of risk-factors, not elsewhere classified (Z91: for example, personal history of unhealthy sleep-wake schedule, and the like).
(iv) The Merck Manual, Seventeenth Edition, Section 14, Chapter 173 defines sleep disorders as disorders that affect the ability to fall asleep, stay asleep, or stay awake or that produce sleep-related abnormal behaviors, and the like. According to the Manual, sleep disorders are classified into the following symptoms: (1) insomnia (disorders falling asleep, difficulty staying asleep, or a disturbance in sleep patterns that causes inadequate sleep, and the like; for example, sleep-onset insomnia (difficulty falling asleep), early morning awakening, sleep-wake reversals, rebound insomnia, and the like); (2) hypersomnia (defined as a pathological increase of at least 25% in total sleeping time; for example, narcolepsy, sudden episode of sleep, and the like); (3) sleep apnoea syndromes, parasomnias (based on patients' chief complaints); and the like.
(v) In actual clinical treatment, sleep disorders are broadly classified into (1) insomnias, (2) hypersomnia, (3) parasomnias, and (4) disorders of sleep-wake schedule (corresponding to the circadian rhythm sleep disorders of ICSD). These classifications are made symptomatically based on patients' chief complaints, separately from the international classifications described above. Depending on etiology, a different medical treatment is given to each type of the sleep disorder.
Given a wide variety of symptoms and etiology of sleep disorders, a holistic approach has been proposed for the adjustment of sleep-wake schedules depending on symptoms and etiology, using non-drug therapy in combination with, for example, (i) for the symptoms of insomnia, drugs that help induce sleep or deepen sleep at nighttime, and the like (for example, sedative hypnotics, psychoactive drugs, antidepressants, and the like such as barbiturates and benzodiazepines), and (ii) for the symptoms of hypersomnia, drugs that have stimulant activity for daytime sleepiness (for example, such as psychoanaleptics).
Meanwhile, the stimulant activity of caffeine has been known for long. Recently, it has been reported that the stimulant activity of caffeine is regulated by adenosine A2A receptor [see Non-Patent Document 1].
Also, a thiazole derivative having antagonistic activity against adenosine A3 receptor (see Patent Documents 1 and 2), a thiazole derivative having antagonistic activity against adenosine A2B receptor and adenosine A3 receptor (see Patent Documents 3 and 4), a thiazole derivative having antagonistic activity against adenosine A1 receptor and adenosine A2A receptor (see Patent Document 5), a thiazole derivative having antagonistic activity against adenosine A2A receptor (see Patent Documents 6 to 8), and the like are known.    Patent Document 1: WO 99/21555    Patent Document 2: Japanese Published Unexamined Patent Application No. 114779/2001    Patent Document 3: WO99/64418    Patent Document 4: US Published Patent Application No. 20040053982    Patent Document 5: WO03/039451    Patent Document 6: WO2005/039572    Patent Document 7: WO2005/063743    Patent Document 8: WO2006/032273    Non-Patent Document 1: Nature Neuroscience, p. 1, 2005